[46.09] The Discovery of New Wolf-Rayet Star Candidates in the Starburst Galaxy IC10

S. B. Holmes, P. Massey (Lowell Observatory)

IC10 is a Local Group dwarf irregular galaxy described by
Hubble (1936) as ``one of the most curious objects in the
sky". Massey and Armandroff (1995) proposed that it is
currently undergoing a starburst: despite its small size, it
contains 15 spectroscopically confirmed Wolf-Rayet stars,
which is a galaxy-averaged surface density that is as high
as that found in young, massive OB associations. This is
consistent with a comparison of the Halpha luminosity to HI
mass or blue light luminosity (Hunter and Gallagher 1986,
Hunter 1993), which suggests a star-formation rate
comparable to that of NGC 1569, a classical starburst
irregular. However, the relative number of WC-type and
WN-type Wolf-Rayet stars is surprising high given the
galaxy's low metallicity. Does this suggest a peculiar
initial mass function or could some of the weaker-lined
WN-type have been missed in earlier surveys? Here we present
results of a deep Mosaic CCD search for Wolf-Rayet
candidates in IC10 using narrow-band filters optimized for
the detection of Wolf-Rayets. Our results have identified
many new candidate Wolf-Rayets, and comparision with a
neighboring ``control field" suggests that we have found a
minimum of a dozen new Wolf-Rayet stars, and possibly as
mandy as sixty. If spectroscopy confirms the majority of
these, then the WC/WN ratio may well be normal, but the
star-formation even higher than previously thought.

In addition, we have confirmed the candidacy of several
stars proposed to be Wolf-Rayets by Royer et al (2001 A&A
366, L1) based their own interference filter imaging but
never confirmed spectroscopically. The exception are their
``WC9" candidates; none of these were detected in our
survey, causing us to question their surprising result that
late-type WCs were to be found in such a low metallicity
system. This work is being supported by the National Science
Foundation under grant AST-0093060.

The author(s) of this abstract have provided an email address
for comments about the abstract:
massey@lowell.edu